It is well known that polymethylsilsesquioxane is a polymer comprising methylsilsesquioxane units which are a trifunctional organosilicon unit, and can take a fine powder form. One of the present inventors previously found a method for the preparation of a polymethylsilsesquioxane fine powder suitable as a material for electronic parts and an additive for polymers as disclosed in, for example, JP-A-63-77940 and 63-295637 (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
The silicone resin fine powder comprising methylsilsesquioxane units obtained by such a method is composed of minute spherical particles usually having a particle diameter of about 0.05 to 100 .mu.m, and has advantages over silica in having a smaller specific gravity and better slip properties and being excellent in dispersibility into organic resins and organic liquids.
However, since the polymethylsilsesquioxane fine powder is hydrophobic, it has been desired for the fine powder to have moderate hydrophilicity and affinity while having a small specific gravity and good slip properties which are the inherent characteristic of the polymethylsilsesquioxane fine powder.
As an example of treatment of an inorganic powder with a polyoxyalkylene-polysiloxane copolymer,a method for preventing development of microgrits by using titanium dioxide treated with such a copolymer, as a component of a treating agent for resin-coated paper for use in photographic printing is known as disclosed in, for example, JP-A-62-25753. However, no example of the treatment with above-described copolymer of a polyorganosilsesquioxane fine powder is yet known.